1. Field of the Invention
The present invention relates to the railroad industry. More particularly, though not exclusively, the present invention relates to a system for navigating a railroad vehicle car over a set of railroad tracks.
2. Problems in the Art
The largest hazard in the railroad industry is train derailments. Each train derailment can cost a railroad company in excess of $1 million in property damage and repair.
The most common cause of train derailments is faulty railroad tracks. After a length of railroad tracks is used over a long period of time or set on unstable grounds, the rails may not provide the train cars with a solid and even surface. A typical railroad track consists of a pair of parallel iron rails mounted to a plurality of wooden railroad ties placed perpendicular to the rails one after the other. The rails are each secured to the ties. The ties are each placed directly on a ground surface. A number of conditions can cause the rails to become uneven or unsolid. Those conditions include worn ties or rails, settling ground, erosion, faulty construction, and other factors. These conditions can be worse on tracks having a high amount of train traffic or tracks having traffic with heavy loads.
A potential hazard exists when the rails become uneven. When the rails of a railroad track are uneven, a train car traveling over the tracks will tend to lean towards the side of the track with the lower rail. As a train travels along the tracks, the train cars may wobble back and forth because of the uneven rails. This condition is the most common cause of train derailments.
Equipment exists in the prior art to repair railroad tracks that are set on settled ground, worn, or not set properly. One such device is commonly known as a rail tamper which is used to reset railroad tracks. However, rail tampers are very expensive (millions of dollars) and therefore can be prohibitively expensive considering the length of railroad tracks across the country. While isolated spots along railroad tracks can be repaired by tampers, it is not practical to reset entire lengths of tracks.
There is no method known in the prior art to determine where the railroad tracks are hazardous. Even if there were a way to determine if one individual section of tracks were bad, this would have to be determined over very short intervals (a few feet) along the entire distance of the track since one bad spot can cause a derailment.
Another problem in the rail industry deals with the navigation of trains. Since a plurality of trains use the same sets of tracks, a hazard exists when two different trains occupy the same track with a close proximity to each other. In order to reduce the risk of a collision, railroad companies will try to keep track of where each train is in order to avoid collisions. Prior art attempts to navigate trains include using global positioning system (GPS) receivers or transponder/interrogator schemes.
Both of these prior art navigation systems have limitations. With a transponder/interrogator system, a number of transponders are placed on the railroad tracks at certain places along the track. An interrogator device is installed on the train and can determine when the train has passed over a transponder. One common failure with this system is caused by misplaced transponders. This may result from vandalism, maintenance errors, etc. Transponders can also be damaged from dragging equipment or weather conditions. The transponders will also become covered with snow or ice during cold weather seasons. This effects the ability of the transponder/interrogator to function properly. The transponder/interrogator system is also limited by the number of transponders used. It is prohibitively expensive to include enough transponders to achieve a high level of accuracy. To alleviate this problem, prior art systems use devices such as odometers allow the train to estimate where it is when it is between transponders. This still results in a system without the accuracy and reliability desired.
Using a GPS receiver to navigate a train also has disadvantages. The use of GPS receivers as a navigator is limited by terrain, foliage, and satellite geometry relative to the terrain and the vehicle. A GPS receiver will be unable to track satellites when the train is traveling through a tunnel or under a bridge. Similarly, when traveling near mountains, buildings, and track side foliage, the satellites may be blocked from view. As a result, like with the transponders, the user must rely on on-board odometers to determine a current location. In addition to these problems are various problems that are inherent with GPS which are known in the art. Using a GPS receiver as a primary navigator intensifies these problems. A GPS position calculation has a lag time. As a result, the position solution provided by a GPS receiver tells a user where the vehicle was a moment ago rather than in real time. Another problem with GPS systems are the errors resulting from the antenna lever arm problem. A GPS antenna typically is a certain distance away from the GPS receiver. Since the GPS antenna is the collection point of the GPS signals received, the position solution will not accurately describe the position of the GPS receiver or some other reference point. If the geometrical distance between the GPS receiver or reference point and the GPS antenna is known, the position of the reference point may be calculated. However, as a ground based vehicle travels over uneven terrain such as terraces, slopes, ruts, bumps, etc., the actual position of the GPS antenna cannot be determined resulting in erratic GPS position solutions.
Most prior art attempts to use a GPS navigation system attempted to deal with GPS problems by correcting GPS drift and lag time. However no prior art system navigating by GPS has achieved the high accuracy and real time solutions required for applications requiring a high level of accuracy. The prior art attempts have not provided an adequate solution because GPS does not provide a continuous navigation solution. A GPS system will update its position periodically, not in real time, and a lag time is still involved. Another problem with a GPS system is the possibility of a signal dropout of the satellite signals. The accuracy of a GPS system is also limited due to the errors caused by the ionosphere. Another problem with GPS systems is that altitude data provided by a GPS receiver is not precise.